Trump's National Security Adviser Robert O'Brien said Germany and other NATO members "not paying their fair share" of defense spending is breaking up the alliance.
Former National Security Adviser John Bolton became the latest ex-Trump administration official to sign a book deal this week.
The former National Security Adviser also reportedly asserted that Trump's negotiations with Iran and North Korea are "doomed to failure."
"If I was going to the new national security adviser—and I won't be, I'm glad it's General Flynn who has that job and not me," Robert O'Brien said in 2016.
The California attorney has been serving as the Special Presidential Envoy for Hostage Affairs since 2018 and has held a smattering of other government positions since 2005.
The list includes a former deputy national security adviser, Vice President Mike Pence's security aide and a hostage negotiator.
"I offered to resign last night and President Trump said, 'Let's talk about it tomorrow,'" Bolton tweeted 12 minutes after Trump published a tweet implying the National Security Adviser was fired.
Despite the national security adviser's claims, many experts are concerned that Russia has persisted in its attempts to hack the upcoming U.S. midterms.
President Trump will meet Putin on Monday in Helsinki, Finland.
Who is in charge of the national security policy of the United States?
"Trump feels really, really, really, bad about firing him, and he genuinely thinks if the investigation is over Flynn can come back," a White House official told The Daily Beast.
Michael Flynn, Trump's first national security adviser, had alarming contacts with Russians and Turk lobbyists, but still got a top-secret clearance.
McMaster is joining the White House staff with views on Russia, counterterrorism, strengthening the military and other major security issues that diverge not only from those of the Trump loyalists, but also from those the president himself has expressed.
He also named retired U.S. Army General Keith Kellogg, who had been serving as acting national security adviser, as chief of staff to the National Security Council.
Flynn's Jan. 24 interview with the FBI could expose him to charges, since lying to the agency is a felony, but any decision to prosecute would lie with the Justice Department.
Harward was offered the job after Michael Flynn was fired by Trump on Monday for misleading Vice President Mike Pence over his conversations with Russia's ambassador to the United States.
During a feisty press conference, the president claimed that his administration is running like a "fine-tuned machine."
It was not immediately clear if Harward, a former deputy commander of U.S. Central Command who has Navy SEAL combat experience, had accepted the offer, according to sources.
Retired Lieutenant General Keith Kellogg will act as interim national security adviser.
New revelations on the Trump adviser's Russia dealings prompt Democratic demands for his removal.